A variable frequency drive (VFD) is a type of motor controller that drives an electric motor by altering the frequency and voltage of its power supply. The VFD also can control ramp-up and ramp-down of the motor during start or stop, respectively.

Even though the drive controls the frequency and voltage of power supplied to the motor, we often define this as speed control, since it can adjust the motor speed.

VFD can be used to ramp down the frequency and voltage to meet the requirements of the electric motor’s load. As the application’s motor speed requirements change, the VFD can simply turn up or down the motor speed to meet the speed requirement.

In addition, today’s drives integrate networking and diagnostic capabilities to better control performance and increase productivity. savings energy , intelligent motor control and reduction of peak-current drawn are three great reasons to choose a VFD as the controller in every motor-driven system.

Soft starters and across-the-line contactors are less sophisticated types of motor controllers. It is a solid-state device and provides a gentle ramp-up to full speed during start-up of an electric motor.

The most common uses of a VFD are for control of fans, pumps and compressors, and these applications account for 75% of all drives operating globally.

An across-the-line contactor is a type of motor controller that applies the full line voltage to an electric motor.

2. What is the Main Advantage of Using a VFD?

answer :

A variable frequency drive can vary the power supplied to match the energy requirement of the driven equipment, and it explains how it saves energy or optimizes energy consumption.

The VFD can dramatically reduce energy consumption when compared to direct-on-line (DOL) operation, where the motor runs at full speed regardless of the demand. Using a drive, power or fuel savings of 40% are normal. The roll-on effect means that using of drives also the reduces NOx emissions and CO2 footprint of the systems when it’s installed.

3. How does a Variable Frequency Drive work?

answer :

The first stage of a VFD, is the Converter. The converter is comprised of six diodes, which are similar to check valves used in plumbing systems. They allow current to flow in one direction only ; the direction is shown by the arrow in the diode symbol. For example, no matter when A-phase voltage is more positive than B or C phase voltages, that diode will open and allow current to flow. When B-phase becomes more positive than A-phase, then the B-phase diode will open and the A-phase diode will close. The same is true for the 3 diodes on the negative side of the bus. Thus, we get six current “pulses” as each diode opens and closes. This is called a “six-pulse VFD”, which is the standard configuration for current Variable Frequency Drives.

4. Why Should I Use a VFD?

answer :

the first reason is that : Reduce Energy Consumption and Energy Costs

If your application doesn’t need to be run at full speed, then you can cut down energy costs by controlling the motor with a variable frequency drive, which is one of the benefits of Variable Frequency Drives. VFDs allow you to match the speed of the motor-driven equipment to the load requirement. There is no other better method of AC electric motor control that allows you to achieve this.

Electric motor systems are responsible for more than 65% of the power consumption in industry today. Combining energy efficiency, tax incentives, and utility rebates, returns on investment for VFD installations can be as little as 6 months. Optimizing motor control systems by installing or upgrading to VFDs which can reduce energy consumption in your facility by as much as 70%. Additionally, the utilization of VFDs improves product quality, and reduces production costs.

2 - Increase Production Through Tighter Process Control

By operating your motors at the most efficient speed for your application, fewer mistakes will occur, and thus, production levels will increase, which earns your company higher revenues. On conveyors and belts you eliminate jerks on start-up allowing high through put.

3 - Extend Equipment Life and Reduce Maintenance

Your equipment will last longer and will have less downtime due to maintenance when it’s controlled by VFDs ensuring optimal motor application speed. Because of the VFDs optimal control of the motor’s frequency and voltage, the VFD will offer better protection for your motor from issues such as electro thermal overloads, phase protection, under voltage, overvoltage, etc.. When you start a load with a VFD you will not subject the motor or driven load to the “instant shock” of across the line starting, but can start smoothly, thereby eliminating belt, gear and bearing wear. It also is an excellent way to reduce and/or eliminate water hammer since we can have smooth acceleration and deceleration cycles.

5. What are the differences between a variable frequency drive (VFD) and a variable speed drive (VSD)?

answer :

A VDF refers to AC drives only and a variable speed drive?(VSD) refers to either AC Drives or DC Drives. VFDs vary the speed of an AC motor by varying the frequency to the motor. VSDs referring to DC motors vary the speed by varying the voltage to the motor.

6. Can You Run a 3 Phase Motor on a Single Phase ?

answer :

YES. You can run a 3 phase motor from standard 220 Single phase power. To be honest. It is an old technique, it is mostly known to old tinkerers and the like. If you are looking for a modern solution, look at our AC Drive control panels that can also run 3 phase motors on single phase power including 120VAC wall outlets.

First, you get the 3 phase motor turning it (manually, or better, with a small 110 v motor), next you can turn on the 220 . It will not run at rated power, or smoothly, but it will run at speed. This is fine for some machines. Now for a magic trick.

take a second (free, same size or smaller) 3 phase motor, and connect it to the first (three leg switch, and zing!, the second motor turns on instantly, and both motors run smoothly!, with more HP than with just 220. The first motor is acting like a "generator" to provide the third leg. This is not "full three phase power", but it works quite nicely. The 220 supplies power to both motors, with one more wire to connect them. You can can connect additional motors also.

This works best if the first motor is a larger HP (2 vs 1), or higher speed rating (3400 vs 1750) than the slave. Older, "beefy" motors are preferable, due to their mass. A 3 HP, 3400 RPM motor works nicly. The reason for this is that if you try to start a bigger load than your master motor, you may reverse the rotation direction of the master (3 phase motors can be wired to run either direction). A large/fast motor will have enough momentum to resist changing directions. The more motors you get running, the more stable the system becomes. The limit may be the amount of power drawn through the third leg of any given motor, the wiring, or your switch, etc.

7. How does a VFD Work on a Pump?

answer :

It controls the frequency of the electrical power which is supplied to a pump or a fan. Important power savings can be accomplished when using a VFD. A VFD is a system use for controlling the rotational speed of an alternating current electric motor. Using a variable frequency drive to control the flow means no additional restriction is added to the piping. Therefore, the system curve remains the same. Varying the speed with a variable frequency drive has the same effect as installing a different-size impeller on the pump: a new pump curve results.

8. Does a VFD Change Voltage?

answer :

A variable-frequency drive (VFD) transforms the mains inputs of constant voltage and frequency into a voltage and frequency range that can be varied to control motor torque. ... The input diodes provide constant dc buffer for the switching inverter section, equivalent to 1.414 times the peak of the input voltage.

9. What is the Difference Between Motor and Drive?

answer :

A drive is the electronic device that harnesses and controls the electrical energy sent to the motor. The drive feeds electricity into the motor in varying amounts and at varying frequencies, therefore controlling the motor's speed and torqueindirectly. ... Together, a motor and drive form a “drive system.”

10. How a VFD Changes Both Voltage and Frequency to Control the Speed of AC Motor?

answer :

Variable frequency Driver is an electronics device that contains VFD panels attached with an AC motor that can efficiently change the fixed voltage and fixed frequency to variable voltage and variable frequency - thus allowing them to be used in different output devices.

It works in following three ways :

1: It is the Rectifier Stage where a diode based rectifier changes a 3-phase 50Hz power received from a 440 or 220 Volt power to an adjustable DC voltage.

2: It is the Inverter Stage where IGBT, SCR, or GCO type of switch is used to switch on or off the DC voltage received from the Rectifier. It forms a current perfect for the ACX motor.

3: It is the Control Stage where the output power that the motor requires is controlled. It efficiently maintains a fixed ratio of voltage to frequency.

11. What Causes Overvoltage on a VFD?

answer :

The most common time when a VFD overvoltage fault occurs is during deceleration. Sometimes the braking torque requirement exceeds drive braking circuit capacity. Other times the deceleration is too fast for its load and inertia from the load is going faster than the designated frequency

12. Does VFD Improve Power Factor?

answer :

A variable frequency drive (VFD) will improve the system power factor, to which it is connected, primarily because the motor reactive current is supplied by the DC bus, rather than the supply system. This will only improve the displacement power factor

13. Why do We Use IGBT in VFD?

answer :

An IGBT will switch the current on and off rapidly so that less voltage will be channeled to the motor, the IGBT can help to create the PWM wave.and the PWM wave is important to a VFDs operation because it is the variable voltage and frequency created by the PWM wave that will allow a VFD to control the speed of the motor

14. How does VFD Improve the System Power Factor?

answer :

A variable frequency drive (VFD) will improve the system power factor to which it is connected, primarily because the motor reactive current is supplied by the DC bus, rather than the supply system. This will only improve the displacement power factor. Modern VFDs with AFE draw almost sinusoidal current from the supply, so power factor on the source side can be controlled up to unity and the generated harmonics are minimal so the system distortion power factor is not greatly affected either. The sole purpose of the DC bus capacitors (in a VSI drive) is to supply the motor load reactive power, not to improve the distribution system power factor, although this is a beneficial consequence. Do not add capacitors to the DC bus of a single unit VFD, this is only sensible if your system employs a common DC bus and you are engineering VFD upgrades and additions.

15. What is a VFD Fault?

answer :

It's known that common fault parameters is key to prevention. Whether a stock VFD in fans, conveyors, and cooling towers, or a specialized unit designed for presses, routers, lathes, roll-forming machines, and extruders, a VFD will generate a low-voltage fault when the voltage drops below set parameters.